Process for the preparation of high-molecular polymerization products

ABSTRACT

A process for producing polymers by the ionogenic polymerization of lactams is disclosed, wherein the lactam monomer, in the liquid state, mixed with a catalyst and promoter is introduced into a heated mold, which rapidly rotates about an axis outside the mold, via a conduit disposed co-axially with respect to the axis and via a feed channel which extends from the conduit at an angle to the axis and the polymerized, molded object is automatically removed from the mold in a radial direction due to centrifugal force.

United States Patent 1191 Zijp et al.

PROCESS FOR THE PREPARATION OF HIGH-MOLECULAR POLYMERIZATION PRODUCTSInventors: Jan W. H. Zijp; Hendrik Bosch;

Antonius Stevenhagen, all of Geleen, Netherlands Stamicarbon N.V.,Heerlen, Netherlands Filed: Oct. 21, 1970 Appl. No.: 82,728

Related US. Application Data Continuation-in-part of Ser. No. 750,741,Aug. 6, 1968, abandoned.

Assignee:

Foreign Application Priority Data Aug. 9, 1967 Netherlands 6710935 U.S.CI 264/311, 264/297, 264/334, 264/DIG. 56, 425/435, 425/436 Int. Cl.B291: 5/04 Field of Search 264/334, 336, 297, 264/310-3111, DIG. 56;l8/26 RR; 25/41 H,

References Cited UNITED STATES PATENTS Rhodes 264/328 June 26, 19733,309,439 3/1967 Nonweiler 264/31 1 3,448,086 6/1969 Bachman et al.264/311 2,454,847 11/1948 Slack, Jr. 264/311 3,164,654 1/1965 Spencer264/311 FOREIGN PATENTS OR APPLICATIONS 1,217,590 5/1966 Germany 264/311Primary Examiner-Donald J. Arnold Assistant Examiner-Gene AuvilleAttorney-Cushman, Darby & Cushman [57] ABSTRACT A process for producingpolymers by the ionogenic polymerization of lactams is disclosed,wherein the lactam monomer, in the liquid state, mixed with a catalystand promoter is introduced into a heated mold, which rapidly rotatesabout an axis outside the mold, via a conduit disposed co-axially withrespect to the axis and via ,a feed channel which extends from theconduit at an angle to the axis and the polymerized, molded object isautomatically removed from the mold in a radial direction due tocentrifugal force.

6 Claims, 8 Drawing Figures Patented June 26, 1973 3,742,109

3 SheetsSheet 1 jZ/wwmes Patented June 26, 1973 3,142,109

3 Sheets-Sheet 2 3 zwam Q /mw A I EA/[YS Patented June 26, 1973 3Sheets-Sheet 5 FIG.

/ I xvi V5945 PROCESS FOR TI IE PREPARATION OF HIGH-MOLECULARPOLYMERIZATION PRODUCTS CROSS-REFERENCE TO RELATED APPLICATION This is acontinuation-in-part application of our earlier United States patentapplication, Ser. No. 750,741, filed Aug. 6, 1968 now abandoned.

BACKGROUND OF THE INVENTION The preparation of high-molecular weightpolymerization products by ionogenic polymerization of lactams, in aprocess wherein a mixture of monomer, catalyst and promoter isintroduced into a heated polymerization mold, is known to the art.

In such a process the volume of the material in the mold decreasesconsiderably, and itis consequently difficult when producing a series ofobjects in the same mold to obtain molded objects having the samedimensions. Another disadvantage is that during the shrinkage of thematerial, a partial vacuum is produced in the mold, as a result ofwhich, air may be drawn in which may cause oxidation with consequentdiscoloration of the surface of the molded object. In most instances itis therefore necessary to maintain a nitrogen atmosphere around the moldduring the polymerization step.

It has previously been suggested to effect the polymerization reactionpartly outside the polymerization mold, so that shrinkage inside themold is reduced. This method has the disadvantage however that theviscosity of the reaction liquid increases substantially during thepre-polymerization step, and may become so high due to the rapid actionof the promoter, that the liquid becomes unsuitable to completely fillthe polymerization mold, and/or air cannot escape quickly enough fromthe mold.

SUMMARY OF THE INVENTION The polymerization mold for lactampolymerization is rapidly rotated about an axis disposed outside themold, and during rotation the lactam to be polymerized is introducedinto the mold by a conduit disposed coaxially with respect to the axis,and by a feed channel which extends from the conduit at an angle to theaxis. The centrifugal force exerted on the lactam, which is in theliquid phase and contains a catalyst and a promoter, is considerablylarger than the force of gravity, thus allowing the mold. to becompletely, filled and vented, with compensation for polymerizationshrinkage. The polymerized, molded object is then automatically removedfrom the mold in a radial direction due to centrifugal force.

DETAILED DESCRIPTION OF THE INVENTION According to the presentinvention, the mold is rapidly rotated about an axis disposed outsidethe mold and during this rotation the material to be polymerized isintroduced into the mold via a conduit disposed coaxially with respectto said axis and via a feed channel which extends from the conduit at anangle to the axis. Preferably the feed channel is radially orsubstantially radially connected to said conduit, although it is onlynecessary that the feed channel projects from the conduit. Uponcompletion of the polymerization reaction, the mold may be stopped andthe polymerized, molded object removed therefrom. Preferably, however,the mold is opened during the rotation of the molds with the aid ofsuitable means as known in the art, whereby the molded object is thrownout of the mold by centrifugal force, and caught; whereupon, the mold isthen closed and a further molded object produced.

During the filling of the rotating mold, the centrifugal force acting onthe mold contents is generally considerably greater than the force ofgravity, and as a result the mold is completely filled and properlyvented. The decrease in volume of the material which occurs during thepolymerization step is compensated for by the fact that notwithstandingincrease in viscosity of the polymerization mixture, the reaction liquidin the feed channel, due to the large centrifugal force exerted on it,fills up the shrinkage void as it is formed.

Molded objects produced by the process of the present invention are veryhomogeneous throughout their mass, and in series production there willbe hardly any differences in dimensions between successive objectsproduced from the same mold. Furthermore, due to the fact that no air isdrawn into the mold during the polymerization step, there is nodiscoloration of the surface of the molded, object, and consequentlythere is no need to effect the polymerization in an inert atmosphere. I

The material to be polymerized is preferably supplied at a temperaturewhich is lower than the temperature of the mold wall, preferably atleast 20 C. below the mold wall temperature, whereby polymerizationstarts near the said walland progresses towards the center of the filledmold. The resulting tendency to forma shrinkage void in the center ofthe object during polymerizaion is overcome by the supply ofpolymerization material into the shrinkage cavity under the influence ofthe centrifugal force acting upon the material in the feed channel.

The volume of polymerization mixture supplied preferably exceeds themould volume by at least 10 percent, but does not exceed the totalvolume of the mould and feed channel. Thus if the polymerizationshrinkage normally amounts to not more than 10 percent, which can beexpected with lactams, the mould will then always be completely filledupon completion of the polymerization, any excess material being presentexclusively in the feed channel. Upon completion of the polymerization,the moulded object may easily be removed from the mould together with ashort sprue, which is removed at a later stage.

From experience in metal rotating-casting techniques in which the moltenmetal is introduced into a rotating drum of lower temperature than themelting point of the material, it would have been reasonable to expectby one in the art, taken into account the fact the temperature of themould considerably exceeds, preferablyby at least 50 C., the meltingpoint of the material supplied, that sealing troubles would arise whenthe monomer, which has the approximate viscosity of water at theelevated temperature, is subjected to large centrifugal forces in themould. It has surprisingly been found however that there is in fact noappreciable leakage of the polymerization material along sealing faces.This may be due to the fact that as soon as the monomer penetratesbetween the said faces, the thin liquid layer present between two heatedwall sections immediately polymerizes and as a result hermetically sealsoff the gap between the faces.

The present invention will be further described with reference to theaccompanying drawings and the following example In the drawings:

FIG. 1 is a longitudinal section through apparatus according to theinvention.

FIG. 2 is a cross sectional elevation of one embodiment of apparatusaccording to the present invention.

FIG. 3 is a partial cross section end view of the mold members of FIG.1.

FIGS. 4, 5, 6, 7 and 8 are schematic diagrams demonstratingseveralalternative modes of moving the cover plates of the molds ofFIGS. 1 and 2.

Referring to FIG. 1, a furnace 1, adjustable so as to provide therequired temperature by means of electrical heating elements 2, containsa number of molds-3. The molds are fitted on a rotating disc 6 carriedon the end of shaft 7 by means of clamp plates 4 and bolts 5.

The shaft 7 is mounted externally of the furnace on bearings 8 and 9mounted in frame 10. The shaft is driven by an electric motor 11 via abelt transmission 12. A number of molds is arranged side by side:parallel to the axis of rotation, each of the molds consisting of twohalves enclosing mold cavities 13, the jointing faces of the mold halvesbeing disposed perpendicular to the axis of rotation of the molds. Thesaid mold cavities 13 connect with the central feed chamber by radialfeed channels 14 and arev uniformly distributed so that the apparatus isbalanced during rotation.

Polymerization mixture is supplied to feed chamber 15 through a feedtube 16 passing through furnace cover 17 and co-axial with the axis ofrotation thereof. The feed chamber 15 is divided into a number ofbiconical sections, each section having its widest diameter near theinlet of one of the connecting feed channels 14. Feed tube 16 is axiallyslideable in cover 17 so that during rotation of the furnace each of thecavities can receive an amount of polymerization mixture depending onthe volume of the mold cavity and the feed channels.-

The molds 3 are open-bottomed and each is provided with an openablecover shown in the figures of the drawings as a rectangular plate 19. Ascan be seen in FIG. 2, the rectangular plates 19 are slideable ingrooves 20 formed in the molds 3. The grooves 20'also hold the slideableplates 19in place during the rotation of the molds 3. The plates 19 areslideable in a direction parallel to the axis of rotation of the molds3. The cover plates 19 are provided with a plurality of oepnings 23 ofsuch size and arranged in such a manner so that when the plate 19 ismoved'in an axial direction the openings 23 come into registration withthe bottom of mold cavities 13, thus opening the bottom of mold cavity13. The plate 19 can then be moved back so that the openings no longerare registerable with the bottom of mold cavities 13 and the plate 19thus forms the bottom face of mold cavity 13.

Several means for sliding the cover plate 19 can be used. In FIG. 2there is shown an electro-magnet relay comprising a magnetic filedinducing coil 35 which when energized through slide contact 37 urges theis supplied through a central bore in the drive shaft of plunger 38,which is integrally connected to cover plate 19, towards coil spring 36.When the coil 35 is deenerthe apparatus shown in FIG. 1 nnd then througha distribution system in clamp plates 4 to the mechanism 25.

In FIG. 5, the cover plate 19 is moved mechanically. A shiftingmechanism 27 as is commonly used in actuating friction clutches isattached to cover plate 19 and extends through furnace cover 17, axiallyarranged around the feed tube 16. The mechanism 27 is moved back andforth by the lever arm 26.

In FIG. 6, a pair of wheeled pushers 28 are actuacte from outside thefurnace cover 17 to push the connecting ring 29 in the desired directionand thus move cover plate 19 which is integrally attached to theconnecting ring.

In FIG. 7, there is shown a modification of the apparatus of FIG. 6,wherein the connecting ring 29 is slotted. The ring 29 rotates with themolds and is connected to the mold clamp plates 4 by a plurality ofsprings 32. The slotted ring 29 can be made to rotate relative to themold by braking mechanism 38. Cover plate 19 is provided with aprolongation which engages with pin 30 in a slot 31 of ring 29. When thebraking mechanism 38 is actuated the ring 29 moves relative to the moldsand pin 30 slides in slot 31 simultaneously moving cover plate 19 to itsopen position. When the braking mechanism is deactivated, springs 32cause ring 29 to rotate back to its original position relative to themolds and thus, cover plate 19 moves back to its closed position.

Instead of the slot and pin as shown in FIG. 7, a nut and screwmechanism can be used as shown in FIG. 8. In this modification, the ring29 is provided withteeth on its inner side which engage teeth on theouter periphery of nut 33. As the ring 29 moves relative to the mold(produced by the braking mechanism as in the apparatus of FIG. 7), nut33 rotates relative to ring 29 and thus, moves cover plate 19 from itsclosed position to its open position and back to its closed position bymeans of bolt 34 screwed in nut 33.

As shown in FIG. 3, the width of mold cavity 13 must increase towardsthe outer periphery of the mold to allow the molded objects to bereleased from the mold when the cover plate 19'is openedfThe moldedobjects are thrown out of the mold cavities 13 by centrifugal force andcollected at the bottom of the furnace, from where they are removed. v

The following example of the apparatus and process of one preferredembodiment of the present invention is provided.

EXAMPLE A suitable polymerization mixture was prepared by adding from0.1 to 2 mole-percent potassium caprolac- .tam calyst and from 0.05 to 2mole-percent dicaprolactim ether to g-caprolactarn. The resulting liquidreac tion mixture was heated to C. A portion of the reaction mixture wasfed to a first set of eight rotating molds having the cover plates 19inthe closed position as shown in the apparatus according to FIG. 2. Theset of eight molds had a total volume of 1,000 cc. and the feed channelsassociated with this set of molds had a total volume of 200 cc.Approximately 1,200 cc. of reaction mixture was fed to this set of moldsthrough feed tube 16, and subsequently the feed tube was shifted and theother two sets of molds were filled with a like amount of reactionmixture. The molds were heated and held at 175 C and rotated at a rateof 300 rev./minute. The average distance between the mold and the axisof rotation was cm., so that a centrifugal acceleration of about 200m/sec or about 20 times the acceleration of gravity was generated.

After about 5 minutes, the polymerization reaction inside the molds wascompleted and the cover plates 19 moved to their open position. Theshaped articles were thrown out of the mold cavities, after which thecover plates 19 were returned to their closed positions and the moldcavities once again were filled with a mixture of the above reactants.

The molded objects from several such cycles were collected at the bottomof the furnace and did not show any air inclusions or shrinkage cavitiesand their surfaces had not been discolored by air oxidation. All themolded objects, of the same shape, were found to possess the samedimensions.

From the above example, it can be seen that the monomer is introducedinto the molds at a temperature somewhat lower than the meltingtemperature of the polymer being formed and higher than the meltingtemperature of the monomer. In the example, caprolactam monomer having amelting point about 156 F. was introduced into the molds at atemperature somewhat below the melting temperature of polycaprolactam(about 410 F As the monomer polymerizes it also solidifies without thenecessity of cooling the mold. The molds are held constantly at thetemperature of the caprolactam feed or somewhat higher but less than thetemperature of the melting point of the polymer being formed. The moldsare kept in constant rotary motion and need not be stopped after formingeach set of molded articles.

The process according to the invention is particularly suited for theseries production of molded nylon articles, such as for examplegearwheels. However, the invention can be employed in the polymerizationof cyclic amides, such as for example butyrolactam, valerolactam,caprolactam, oenantholactam, capryllactam, decanolactam, undecanolactam,laurinolactam, pentadecanolactam, hexadecanolactam, methyl caprolactam,cyclic hexamethylene adipamide and mixtures thereof, in the presence ofan ionogenic catalyst, such as for example lactammetal compoundscontaining a metal atom which is bound to the lactam-nitrogen I atom,e.g., sodium caprolactam, and potassium caprolactam. The lactam-metalcompound may conveniently correpond to the lactam being polymerized. Inthese polymerization processes, use can be made of sub stances whichreact with the lactam to form such lactam-metal compounds, e.g.,metal-alkyl compounds, such as for example diisobutyl aluminium hydride,triethyl aluminium, triisopropyl aluminium, diethyl zinc and compoundsof these metals giving an alkaline reaction, such as for examplehydrides, oxides, hydroxides, alcoholates and carbonates, and alsoGrignard compounds, such as alkyl magnesium bromide and aryl magnesiumbromide.

Nitrogen compounds, such as isocyanates, carbodiimides, cyanamides andin general compounds having a tertiary nitrogen atom which is bound tocarbonyl, thiocarbonyl, sulphonyl or nitroso groups, and also 'diimideethers, such as dicaprolactim ether, can be used as the promoter.

Fillers such as anti-oxidants, UV-stabilizers, pigments, dyes, glass ortextile fibers, coated or uncoated and inorganic auxiliary materials,may be added to the reaction liquid. It is furthermore possiblesuccessively to charge the mold with different lactams, which may, if sodesired, be mixed with fillers particularly if it is required that theproperties of the material at the surface of the object differ fromthose at the core.

Generally, the liquid lactam to be polymerized will contain from about0.1 to 2.0 percent by weight of the catalyst and about 0.01 to 3.0percent by weight of a promoter, as is known to the art. The mold walltemperature is, as mentioned above, held constant at generally about to180 C., preferably about to C The polymerization is convenientlyconducted at atmospheric pressure although higher or lower pressures maybe used as desired.

The rotational speed of the mold should be such that the resultantcentrifugal force exerted upon the material to be polymerized is greaterthan the force of gravity, preferably at least five times the force ofgravity, and most preferably the centrifugal force caused by the moldrotation is at least 10 times the force of gravity acting upon thelactam.

What is claimed is:

1. In a process for the manufacture of high molecular weight,polymerized, molded objects by ionogenic catalytic polymerization oflactams,- wherein at least one lactam monomer, mixed with a catalyst andpromoter for accelerating the polymerization, in the liquid state, isintroduced into a heated mold in which the polymerization occurs, theimprovement comprising using a mold having a width which increasestoward the outer periphery of the mold and rapidly rotating the 'mold onan axis outside the mold, introducing the lactam to be polymerized intosaid mold at a position on said mold nearest said axis, said mold beingrotated at such a speed that the resultant centrifugal force exertedupon the lactam to be polymerized is greater than the force of gravity,polymerizing said lactam in said rotating molds and removing said moldedobjects by opening the outer periphery of said mold thereby permittingthe molded object to be thrown in a radical direction from the moldcavity by centrifugal force.

2. A process as claimed in claim 1 wherein the lactam to be polymerizedis introduced into said mold via a conduit disposed co-axially withrespect to said axis, and via a feed channel which extends from theconduit at an angle to the axis.

3. The process as claimed in claim 1, wherein the rotation speed of saidmold is such that the resultant centrifugal force exerted upon thelactam to be ized is at least five times the force of gravity.

4. The process asv claimed in claim 1, wherein the rotation speed ofsaid mold is such'that the resultant centrifugal force excerted upon thelactam to be polymer-.

ized is atleast 10 times the force of gravity.

5. The process as claimed in claim 1, wherein the lac tam to bepolymerized is supplied at a temperature which is lower than thetemperature of the wall of the mold.

6. The process as claimed in claim 1, wherein the temperature of thelactam to be polymerized is at-least 20 C. less than the temperature ofthe wall of the mold.

polymer-

2. A process as claimed in claim 1 wherein the lactam to be polymerizedis introduced into said mold via a conduit disposed co-axially withrespect to said axis, and via a feed channel which extends from theconduit at an angle to the axis.
 3. The process as claimed in claim 1,wherein the rotation speed of said mold is such that the resultantcentrifugal force exerted upon the lactam to be polymerized is at leastfive times the force of gravity.
 4. The process as claimed in claim 1,wherein the rotation speed of said mold is such that the resultantcentrifugal force excerted upon the lactam to be polymerized is at least10 times the force of gravity.
 5. The process as claimed in claim 1,wherein the lactam to be polymerized is supplied at a temperature whichis lower than the temperature of the wall of the mold.
 6. The process asclaimed in claim 1, wherein the temperature of the lactam to bepolymerized is at least 20* C. less than the temperature of the wall ofthe mold.